Epidemiologicalstudiesindicatethatchemotherapycanincreasethechanceofmetastasisinasubsetpatients, buttheunderlyingmechanismremainsunclearbecauseofalackofrelevantexperimentalmodels.Thegoalof this proposal is to elucidate the impact of chemotherapy on metastatic relapse with a tissue-engineered metastasis model that can capture metastaticniche evolution with a high level of molecular and cellular detail. Inspired by the recent discovery of the pre-metastatic niche (PMN) in major metastatic organs, we have developed a bone marrow stromal cell?seeded microfabricated porous hydrogel scaffold that creates a richly vascularizedproinflammatorymicroenvironmentwhenitissubdermallyimplantedinamouse.Thisimplantable PMN model hasbeen showntoattractand support theengraftmentand growth of circulatingtumor cellsand can be serially implanted in syngeneic naive mice for long-term studies. The semitransparent materials of the implant are compatible with quantitative imaging analysis via multiple imaging modalities including multiplex immunohistostaining,CLARITY-basedopticalsectioningofentirescaffolds,andintravitalimagingviaaskinfold windowchamber. Our central hypothesis is that tissue inflammation and remodeling induced by chemotherapy activates dormant disseminated tumor cells and causes them to migrate and form in situ clusters as a function of cell number. Forming clusters could allow the cells to overcome microenvironmental regulation and regain an aggressive phenotype. Weproposethreespecific aims: In Aim 1, we will generate subcutaneousand hepatic PMNmodelsinaMMTV-PyMTfemalemouseanddemonstratethelong-termevolutionofmetastaticnicheby seriallytransplantingearlymetastaticnicheestablishedinprimarymicetosecondarysyngeneicFVBmice.For this purpose, we will generate MMTV-Luc2-PyMT mice that allow non-invasive long-term bioluminescent monitoring of metastatic relapse. InAim2, we will use the techniques verified in Aim1 toobserve the effectof chemotherapy with doxorubicin on the metastatic process in serially implanted bone marrow and liver PMN models. In Aim3, we will applytheestablished algorithmto measure potencytodetermine ifadjuvant therapy with anti-inflammatory (anakinra) or anti-macrophage (clodronate) drugs reduces doxorubicin-induced metastaticrelapseandwilllookattheeffectofadjuvanttiming.Theproposedresearchissignificantbecauseit hasthe potential to facilitate thedevelopmentofbetter therapeutic regimensthat caneliminateactive residual tumorcellswithoutactivatingdormantdisseminatedtumorcells,andthiswouldsignificantlyimprovelong-term metastasisprevention.